The updates to other extensions may have updated shared files that are causing Site Import not to work.
We never made any updates to Site Import V2 for CS4 compatibility, nor have we done any testing on that platform. Dreamweaver CS4 is not a platform we offer support for Site import V2.
That is not to say that it didn't work for you in the past, but where it is not working now, we cannot offer support since there were no updates made for CS4 support or testing.
Before Dreamweaver CS4 was released, we released Site Import 3, site Import 3 was made to be compatible with Dreamweaver CS4, and was tested with that platform.